Objective C: How do I draw lines with alpha in quad curve - iphone

Question

I'm having trouble in points when i'm using a quad curve point.. I want to set the opacity to my lines but i also see points here it is..
here are my codes..
CGPoint midPoint(CGPoint p1,CGPoint p2)
{
return CGPointMake ((p1.x + p2.x) * 0.5,(p1.y + p2.y) * 0.5);
}
-(void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event//upon touches
{
UITouch *touch = [touches anyObject];
previousPoint1 = [touch locationInView:self.view];
previousPoint2 = [touch locationInView:self.view];
currentTouch = [touch locationInView:self.view];
}
-(void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event//upon moving
{
UITouch *touch = [touches anyObject];
previousPoint2 = previousPoint1;
previousPoint1 = currentTouch;
currentTouch = [touch locationInView:self.view];
CGPoint mid1 = midPoint(previousPoint2, previousPoint1);
CGPoint mid2 = midPoint(currentTouch, previousPoint1);
UIGraphicsBeginImageContext(CGSizeMake(1024, 768));
[imgDraw.image drawInRect:CGRectMake(0, 0, 1024, 768)];
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSetLineCap(context,kCGLineCapRound);
CGContextSetLineWidth(context, slider.value);
CGContextSetBlendMode(context, blendMode);
CGContextSetRGBStrokeColor(context,red, green, blue, 0.5);
CGContextBeginPath(context);
CGContextMoveToPoint(context, mid1.x, mid1.y);
CGContextAddQuadCurveToPoint(context, previousPoint1.x, previousPoint1.y, mid2.x, mid2.y);
CGContextStrokePath(context);
imgDraw.image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsGetCurrentContext();
endingPoint=currentTouch;
}
any answer will be appreciated.

Answer 1

What you need to do is keep the list of all points the user has entered so far, and always redraw all of them as part of the same path.
You'll need an array to store the points in. Something like
CGPoint points[kMaxNumPoints];
instead of previousPoint1/2, etc. Then in touchesMoved:, you'll iterate over the points in a loop. Something like this:
CGContextBeginPath (context);
CGContextMoveToPoint (context, points [ 0 ].x, point [ 0 ].y);
for (int i = 1; i < currNumPoints; i++)
{
// I wasn't sure from your example if you wanted the mid point here instead of the
// previous point. But you get the idea.
CGContextAddQuadCurveToPoint (context, points [ i - 1 ].x, points [ i - 1 ].y, point [ i ].x, point [ i ].y);
}
CGContextStrokePath (context);